Time-resolved MOKE

Layout of the MOKE setup
Image: Lisa Willig

In order to detect laser-induced magnetization changes in materials with ferroic magnetic order we utilize a cryogenic pump-probe setup exploiting the magneto-optical Kerr effect (MOKE).

Our time-resoved polar MOKE setup works at 1 kHz repetition rate with probe pulses at 400 nm wavelength. The pump pulse wavelength can be varied continuously from 450 nm to 5000 nm using a two-stage noncollinear optical parametric amplifier (NOPA). The pump pulses are chopped at 500 Hz to improve the S/N ratio.

External magnetic fields up to 1000 mT are supplied by an electromagnet. The sample can be placed inside a cryogenic environment for temperature variations from room temperature down to 20 K.

Layout of the MOKE setup
Image: Lisa Willig
Magnetic hysteresis loops of a FePt thin film at various pump-probe delays for several excitation fluences
Image: Lisa Willig

The example shows time-resolved hysteresis loops of a continuous 10 nm thin FePt film for various pump fluences. At the highest fluence, the spin disorder fully supresses the ferromagnetic hysteresis beyond 25 ps. Such hysteresis loop measurements are fully automated including the variation of the pump fluence.

Further details:
Willig et al., Phys. Rev. B 100, 224408 (2019).

Magnetic hysteresis loops of a FePt thin film at various pump-probe delays for several excitation fluences
Image: Lisa Willig